1. Field of the Invention
The present invention relates to a droplet ejection apparatus and an image forming apparatus, and particularly to a head structure for reducing the crosstalk caused by a flow channel structure of a droplet ejection head having a plurality of nozzles (droplet ejection ports) arrayed two-dimensionally, and a drive control technology of the head structure.
2. Description of the Related Art
Japanese Patent Application Publication No. 06-198893 discloses a technology of an inkjet printer having a one-dimensionally arranged nozzle row in which the ejection timings are shifted between adjacent nozzles to prevent resonant oscillation of liquid between the nozzles in order to increase the drive frequency so that the productivity is improved. More specifically, the nozzles in the nozzle row are divided into four nozzle groups of every fourth nozzles. The nozzles in the same nozzle group are caused to simultaneously eject the ink, whereas the phases of the respective nozzle groups are shifted with each other. In this inkjet printer, the positions of orifices (nozzles) are corrected beforehand in order to reduce printing misregistration caused by shifting the ejection timings between the nozzle groups.
Japanese Patent Application Publication No. 09-104113 discloses a technology in which a plurality of recording elements (nozzles) arranged one-dimensionally are divided into a plurality of blocks, and “division record” is carried out in which the recording timings are shifted between the blocks for reducing the increase in crosstalk and power source capacity, which are problems caused when driving all of the nozzles at the same time. Moreover, the shift of the recording timings is slightly changed so as to absorb an angular error generated when attaching line heads.
Japanese Patent Application Publication No. 2007-144751 discloses a technology in which a plurality of nozzles formed in an inkjet head are divided into a plurality of nozzle groups (for example, respective groups of K, C, M and Y), a plurality of images are recorded while shifting the ejection timings between the first nozzle group and the rest of the nozzle groups, and the best image is determined from among these images (that is, the best ejection timing difference), thereby limiting the effects of an ejection variation caused by the crosstalk among the nozzle groups.
A head in which nozzles ejecting droplets are two-dimensionally arrayed has special problems different from those of the one-dimensionally arrayed nozzles in which the ejection timings between adjacent nozzles cannot be shifted due to the drive wiring, for example. Japanese Patent Application Publication No. 06-198893 does not mention any countermeasures for crosstalk of the two-dimensionally arrayed nozzles, and the technology described in Japanese Patent Application Publication No. 06-198893 cannot be applied to the two-dimensionally arrayed nozzles. The recording head described in Japanese Patent Application Publication No. 09-104113 has a plurality of recording elements arranged in a single row, and causes shifting in the timings for the respective blocks with respect to the inclination of the entire head. Therefore, the “vertical line” formed by the entire line head is averagely straight, but jagged lines are generated in the vertical rule, as shown in FIG. 10(c) and described in the paragraph 0040 in Japanese Patent Application Publication No. 09-104113, which causes a problem in the image quality. In the technology described in Japanese Patent Application Publication No. 2007-144751, shifting of the ejection timings changes the droplet deposition positions and thereby causes, for example, positional difference (color difference) between the colors, but such a problem is not mentioned.